1. Field of the Invention
The present invention relates generally to a plasma pinch chamber, and more specifically to a nested, two-tube chamber used in connection with a high-Z, high-density, laser-guided, gas-embedded pinchlamp device.
2. Description of Related Art
In response to a variety of deficiencies in flashlamp technology, the next generation of high-power radiation resources evolved, that being the pinchlamp. One example of such a pinchlamp is the liquid-jet pinchlamp disclosed in U.S. Pat. No. 4,889,605 to Asmus et al. The chamber structure is basically a sealed tube. The liquid-jet pinchlamp is designed to shoot a thin stream or jet, generally 100 xcexcm, of liquid decane into a vacuum chamber. As the decane traverses the chamber, a small amount of the liquid evaporates, creating a tenuous vapor cloud around the jet. A high electrical potential then is applied from one end of the jet to the other, and a small electrical current flows through the cloud in the chamber. The UV radiation from the cloud heats the liquid decane to the point of electrical conduction. Then a very large electrical current flows through the newly created conducting liquid, and heats it to very high temperatures so that high-intensity radiation is produced.
Another type of pinchlamp, the laser-guided gas-embedded pinchlamp, is somewhat similar to the liquid-jet pinchlamp, but improves upon the liquid-jet pinchlamp as it is free of the vacuum pumping element required in the liquid-jet pinchlamp device. Generally, a gas-embedded pinchlamp device comprises high pressure Argon gas contained within a large quartz chamber or tube. A beam from a very small laser is directed down the axis of the tube, and creates a straight and narrow, generally 5 mm in width, conductive path for a high power electrical discharge. The electrical discharge heats the dense Argon channel to a very high temperature, producing plasma.
Although several pinchlamp designs exist, most that utilize a high-temperature plasma require a suitable container or chamber to confine the plasma. Such confinement of the plasma is achieved by various techniques, which confinement devices are generally referred collectively to as a xe2x80x9cplasma pinchxe2x80x9d. A plasma pinch is so called because the magnetic forces generated by the electric current through the plasma channel serve to pinch or compress the plasma toward its axis. The magnitude of the pinch effect is dependent upon the magnitude of the current creating the pinch. It is possible to select the current so as to form a stable pinch in which the thermal expansion of the plasma particles is generally offset by the pinch effect so that the plasma channel diameter remains substantially constant. A much greater current will eventually collapse a pinch to a fine filament.
Radiation is emitted relatively uniformly throughout the duration of a stable pinch, whereas, in the case of the collapsing pinch, most of the radiation occurs upon collapse of the pinch. An advantage of the collapsing pinch is that it compresses the electrical energy input into a pulse of relatively short duration. Because of this pulse compression, drive rise time requirements on the electrical system are relaxed. On the other hand, an advantage of the stable pinch is that it does not generate shock waves by sudden transformation of shape.
Plasma pinch systems have been employed for various applications. For instance, U.S. Pat. No. 4,042,848 to Lee describes a hypocyclodial pinch device for producing a dense plasma at thermonuclear fusion temperatures. U.S. Pat. No. 4,406,952 to Molen, et al. describes a switch for interrupting current using a plasma focus device.
In U.S. Pat. No. 4,450,568 to Asmus. there is disclosed a laser preconditioned plasma pinch, which emits vacuum ultraviolet radiation, for dissociating the molecules of a photolytic laser medium confined in a chamber. The preconditioning laser beam excites the gas particles in the vicinity of the chamber axis, for defining a preconditioned channel within which the plasma pinch is formed.
U.S. Pat. No. 4,543,231 to Ohkawa describes a plasma pinch used in fusion devices to produce a toroidal plasma. In U.S. Pat. No. 4,621,577 to Bickes Jr., et al., there is disclosed a plasma pinch formed by a discharge between electrodes, used for detonating explosives.
Another major application of the plasma pinch is its use in X-ray lithography. For example, in U.S. Pat. No. 4,424,102 to Brandeis. et al., a plasma pinch is disclosed and is used for reactive ion etching of semiconductor substrates. The etching process includes the use of magnetic fields in connection with the plasma pinch. U.S. Pat. Nos. 4,504,964; 4,536,884; 4,618,971; 4,633,492; and 4,635,282 also disclose various plasma pinch systems usable in X-ray lithography, whereby X-rays are generated by passing a high current through the plasma.
In U.S. patent application Ser. No. 09/140,645 there is disclosed a method and apparatus for utilizing a laser-guided gas-embedded pinchlamp device for the removal of coatings and contamination from surfaces. That device can be utilized for paint stripping, paint removal, or other coating and contamination removal processes, or in aseptic packaging and medical devices, methods for food preservation, large-area metals and ceramic glazing, semiconductor annealing and biochemical decontamination.
Referring now specifically to the chamber confining the plasma, the typical plasma pinch comprises pressurized gas in a large transparent tube. Alternatively, the pressurized gas is termed the working gas, and the tube referred to as a window. Present devices use a single tube to confine the gas. The hot radiating plasma created during use is prevented from coming into contact with the walls of the transparent tube because of the xe2x80x9cpinchxe2x80x9d caused by the ionization of the gas directly effected by, in the case of a laser-guided, gas-embedded pinchlamp, a laser beam that creates a conductive path for a high powered electrical discharge from electrodes.
The conventional chamber is manufactured from a quartz or sapphire window, and the conventional pressurized gas is Argon. The use of sapphire for the tube, instead of quartz, is particularly desirable for many reasons, including that a higher power is attainable without tube failure. Argon is a preferable working gas because it is a good light-generating gas (electron donating), and is economical.
In maximizing the performance (output power) of a plasma pinchlamp, generally four parameters specific to the plasma pinch architecture must be negotiated. Yet, adjusting these parameters in order to increase the output power of the pinchlamp can be difficult, as the beneficial adjustment of one parameter to maximize performance contradicts the beneficial adjustment of another. The four parameters are as follows:
1. The diameter of the tube that contains the working gas should be maximized so the wall of the tube will be as far as possible from the following so as not to shatter: (a) the heat of the plasma produced, (b) the shock wave from the production of the plasma, and (c) the pressures generated by the plasma.
2. The diameter of the tube that contains the working gas should be minimized so the volume of the working gas, which is both cold and absorbing, is minimized.
3. The working gas in which the pinch is embedded should be a high-Z gas to maximize the useful light output.
4. The working gas in which the pinch is embedded should be a low-Z gas to minimize absorption, and loss, of useful light in the cold surrounding working gas.
As is evident, it is contradictory to simultaneously satisfy both factors 1 and 2, and factors 3 and 4, with a plasma pinch having a single tube (one diameter), containing a single working gas. Yet, more powerful pinchlamps would be advantageous in a number of different applications. Thus, it can be seen that there is a need for the present invention, an improvement over the prior art plasma pinch devices, that satisfies the contradictory demands of a more powerful pinchlamp device than is presently known, by providing a double-wall confinement configuration for a plasma pinch. It is the provision such an inner/outer coaxial tube arrangement for a plasma pinch chamber, and a plasma pinchlamp that utilizes such a chamber, that the present invention is primarily directed.
Briefly described, in a preferred form, the present invention simultaneously satisfies the four contradictory factors of a plasma pinch identified as maximizing the performance of a pinchlamp device, by providing a plasma pinch having an inner/outer coaxial tube arrangement, which nested tube arrangement yields a higher-performance pinchlamp than is capable with a single-tube configuration. Further, each tube contains a separate gas, the inner tube filled with Argon, and the outer tube filled with Helium. The present invention is directed to such a two-tube configuration, and a pinchlamp utilizing a two-tube configuration.
The inner/outer coaxial tube arrangement of the present invention facilitates the use of an inner tube to contain a volume of Argon gas as the working gas. An outer tube, coaxial with the inner tube, surrounds the inner tube with contained Helium gas. The configuration of an outer tube filled with Helium presents a pressure means to apply external pressures to the inner tube. The contained Helium gas in the outer tube, among other things, compresses and supports the wall of the inner tube, enabling the inner tube to be smaller in diameter than prior art plasma chambers, which chambers would shatter if made with as small a diameter as the present inner tube.
The outer tube is but one embodiment of a pressure means to enable the smaller-dimensioned inner tube of the present invention to contain the plasma generation without structural failure.
The plasma pinch of the present invention can comprise more than two tubes. For example, the inner tube could itself be two nested tubes with water between them for cooling. Likewise, the outer tube could be two nested tubes with water in between for cooling.
Therefore, it is an object of the present invention to provide a new and improved plasma pinch.
It is another object of the present invention to provide a new and improved plasma pinch having an inner tube filled with working gas, which inner tube is of smaller diameter than present plasma chambers.
It is a further object of the present invention to provide a new and improved plasma pinch having an inner tube containing a smaller volume of working gas than present chambers, yet which inner tube is manufactured with wall materials and thicknesses currently used in conventional plasma chambers. Although, while conventional chambers would explode in use if produced to the dimensions of the present inner tube, the present plasma pinch provides sufficient pressures to the outer surface of the inner tube wall so as to maintain the integrity of the inner tube during use.
Yet another object of the present invention is to provide a plasma pinchlamp utilizing a two-tube plasma pinch.
It will be apparent to those skilled in the art that the present invention is applicable to a wide range of usages, including flashlamp devices, and is not limited to the present preferred embodiments.
These and other objects, features, and advantages of the present invention will be more apparent upon reading the following specification in conjunction with the accompanying drawing figures.